(GetScreenHeight returns 1050 for me, which is my actual Y-resolution.)

The general technique is still useful if you want to be able to scale frames without scaling certain elements (e.g. 1-pixel border on a scalable map). Or for people who use uiscale but want a certain element to render at pixel scale. That said I'm still not entirely sure what needs to be changed in order for that to work in 4.0.1.